[PATCH] D89632: [DomTree] Accept Value as Def (NFC)

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: asbirlea, kuhar, dblaikie, jdoerfert.
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Non-instruction defs like arguments, constants or global values always dominate all instructions/uses inside the function. This case currently needs to be treated separately by the caller, see https://reviews.llvm.org/D89623#inline-832818 for an example. This patch makes the dominator tree APIs accept a Value instead of an Instruction and always returns true for the non-Instruction case.

A complication here is that BasicBlocks are also Values. For that reason we can't support the `dominates(Value *, BasicBlock *)` variant, as it would conflict with `dominates(BasicBlock *, BasicBlock *)`, which has different semantics. For the other two APIs we assert that the passed value is not a BasicBlock.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D89632

Files:
  llvm/include/llvm/IR/Dominators.h
  llvm/lib/IR/Dominators.cpp
  llvm/unittests/IR/DominatorTreeTest.cpp


Index: llvm/unittests/IR/DominatorTreeTest.cpp
===================================================================
--- llvm/unittests/IR/DominatorTreeTest.cpp
+++ llvm/unittests/IR/DominatorTreeTest.cpp
@@ -1071,3 +1071,32 @@
     EXPECT_TRUE(DT->dominates(E23, E23));
   });
 }
+
+TEST(DominatorTree, ValueDomination) {
+  StringRef ModuleString = R"(
+    @foo = global i8 0
+    define i8 @f(i8 %arg) {
+      ret i8 %arg
+    }
+  )";
+
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+
+  runWithDomTree(*M, "f",
+                 [&](Function &F, DominatorTree *DT, PostDominatorTree *PDT) {
+    Argument *A = F.getArg(0);
+    GlobalValue *G = M->getNamedValue("foo");
+    Constant *C = ConstantInt::getNullValue(Type::getInt8Ty(Context));
+
+    Instruction *I = F.getEntryBlock().getTerminator();
+    EXPECT_TRUE(DT->dominates(A, I));
+    EXPECT_TRUE(DT->dominates(G, I));
+    EXPECT_TRUE(DT->dominates(C, I));
+
+    const Use &U = I->getOperandUse(0);
+    EXPECT_TRUE(DT->dominates(A, U));
+    EXPECT_TRUE(DT->dominates(G, U));
+    EXPECT_TRUE(DT->dominates(C, U));
+  });
+}
Index: llvm/lib/IR/Dominators.cpp
===================================================================
--- llvm/lib/IR/Dominators.cpp
+++ llvm/lib/IR/Dominators.cpp
@@ -115,8 +115,14 @@
 // dominates - Return true if Def dominates a use in User. This performs
 // the special checks necessary if Def and User are in the same basic block.
 // Note that Def doesn't dominate a use in Def itself!
-bool DominatorTree::dominates(const Instruction *Def,
+bool DominatorTree::dominates(const Value *DefV,
                               const Instruction *User) const {
+  const Instruction *Def = dyn_cast<Instruction>(DefV);
+  if (!Def) {
+    assert(!isa<BasicBlock>(DefV) && "Should not be called with basic blocks");
+    return true; // Arguments, constants, globals dominate everything.
+  }
+
   const BasicBlock *UseBB = User->getParent();
   const BasicBlock *DefBB = Def->getParent();
 
@@ -250,7 +256,13 @@
   return dominates(BBE, UseBB);
 }
 
-bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
+bool DominatorTree::dominates(const Value *DefV, const Use &U) const {
+  const Instruction *Def = dyn_cast<Instruction>(DefV);
+  if (!Def) {
+    assert(!isa<BasicBlock>(DefV) && "Should not be called with basic blocks");
+    return true; // Arguments, constants, globals dominate everything.
+  }
+
   Instruction *UserInst = cast<Instruction>(U.getUser());
   const BasicBlock *DefBB = Def->getParent();
 
Index: llvm/include/llvm/IR/Dominators.h
===================================================================
--- llvm/include/llvm/IR/Dominators.h
+++ llvm/include/llvm/IR/Dominators.h
@@ -169,8 +169,10 @@
   ///
   /// This performs the special checks necessary if Def and User are in the same
   /// basic block. Note that Def doesn't dominate a use in Def itself!
-  bool dominates(const Instruction *Def, const Use &U) const;
-  bool dominates(const Instruction *Def, const Instruction *User) const;
+  bool dominates(const Value *Def, const Use &U) const;
+  bool dominates(const Value *Def, const Instruction *User) const;
+  // Does not accept Value to avoid ambiguity with dominance checks between
+  // two basic blocks.
   bool dominates(const Instruction *Def, const BasicBlock *BB) const;
 
   /// Return true if an edge dominates a use.


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